The use of membrane filters for the purification and separation of materials within a fluid stream is a well developed art. As used herein the term membrane filter of filter includes semipermeable membranes formed of a solid polymeric matrix and having a controlled and measurable porosity. These filters are generally fabricated into devices, such as cartridges, which are adapted to be inserted within a fluid stream to effect the removal of particles and/or micro-organisms from liquids and gases.
Depending on the application, membrane filter devices must be compatible with a wide variety of chamicals and solvents. For example, in the manufacture of microelectronic circuits, membrane filters are used extensively to purify various process fluids to prevent contaminants from causing circuit failures and hence reducing manufacturing yields. The process fluids typically used in the manufacture of semiconductors are generally strong (i.e., chamically active) solvents, acids or bases. Therefore, such an application requires the use of a chemically inert filter, for example, a fluorocarbon based filter is often employed. Because these filters are hydrophobic, they are not spontaneously wet by aqueous based process fluids. Hydrophobic membrane filter devices which are intended for use in aqueous applications are generally packaged dry in a plastic bag. Thus the user is often required to pretreat the filter before using it in such process streams. This pretreatment is time consuming, may require the user to provide a separate installation to carry out the pretreatment and can often result in the introduction of contaminants downstream of the filter. Most often the prewetting agent used is alcohol, a flammable liquid, which presents safety concerns. This requires the end user prior to putting the filtration device into service to wet the filter with alcohol, followed by a water flush and then a flush with process solution. While manufacturers of membrane filter devices are accustomed to handling and pretreating hydrophobic filters, end users may not have the capabilities or the desire to perform such additional processing steps. Hence the notions of "user friendly" and "ready the use" are prevailing concepts in the art of membrane filtration.
Although the prevailing means for shipping hydrophobic filters is in a dry plastic bag, certain hydrophobic membranes, particularly ultrafiltration membranes, cannot be dried without damaging their structure. Thus these membranes are shipped wet, usually packaged with water and a preservative, such as glycerin and/or formaldehyde, the preservative serving to prevent the growth of bacteria present in the water. However, the preservative contained within the pore structure of the membrane will leach into the process fluid and can thus contaminate this fluid. Hence this packaging concept requires pretreatment with concomitant special handling by the user and suffers from the disadvantages referred to above. Moreover, elimination of the preservative will greatly reduce the shelf life of the membrane filter device due to high bacteria growth.
Thus the need still exists for an effective transport mechanism for hydrophobic membrane filters. That is a packaging concept which allows the customer to immediately install the membrane filter device in his process stream with minimal risk of contamination and minimal pretreatment would be highly desirable particularly for use in the semiconductor manufacturing industry.